Treatment of uranium ore



Pll 30, 1963 A. D. GARRISON 3,087,780

TREATMENT OF URANIUM ORE Filed Dec. 22, 1958 Ef@ Patented Apr. 30, 1963 3,037,780 TREATMENT F URNIUM ORE Allen D. Garrison, La Jolla, Calif., assignor to Texaco Inc., a corporation of Delaware Filed Dec. 22, 1958, Ser. No. 782,195 4 Claims. (Cl. 23-14.5)

This invention relates to a method of concentrating uranium values of a uranium ore. In one of its more specific aspects it is directed to an improved method of separating Iuranium from its ores by forming a volatilizable and sublimable uranium compound wherein said ore is contacted ywith a fluoride selected from the groups consisting of ammonium fluoride -and `ammonium biuoride at an elevated temperature. Uranyl am-monium pentafluoride, (UO2)(NH4)3F5, is formed and is separated as a vapor from a solid ore residue. Advantageously, the ore and fluoride a-re contacted in the presence of an oxidizing gas, for example, air, so that any tetravalent uranium in the ore is oxidized tothe hexavalent or uranyl form. The uranyl ammonium pentafluoride vapor is recovered by condensation, for example, on cooled metal pipes or walls or by contacting with cool pulverulent solids.

The uranyl ammonium pentauoride is sublimed from the treated ore at :an elevated temperature. A temperature is selected to achieve a satisfactory rate of stripping of the uranium from the ore without exceeding apparatus limitations and the temperature at which natural ingredients of the ore are sintered or melted. Since sublimation pressures iare like vapor pressures and increase in like manner with increasing temperature, the uranyl ammonium pentafluoride is stripped even at temperatures below the point at which the sublimation pressure attains one atmosphere. However in order to eiect rapid and complete stripping, it is preferred to contact the ore and ammonium iluoride at a temperature `of at least 400 F. The upper temperature limit is Wholly independent of sublimation pressure, and is determined by the melting temperature of the ore and by .the limitations of the apparatus. For example, typical uranium ores may be treated at a temperature of about l800 F. Without danger of sintering and obstructing the stripping apparatus.

Uranium ores, as found in nature, usually contain large quantities of quartz and feldspars in the form of individual crystals or grains which contain little or no uranium. The uranium values appear in the cracks, crevices and grain boundaries. The quartz and feldspar are comparatively hard whereas the uranium values appear` as relatively crumbly and soft interstitial films or coatings. For example, the relative hardness of some ofthe minerals found in uranium ores is given in the following table.

Mineral: Mohs hardness Quartz 7 Feldspars 6 to 6.5 Uraninite 5.5 Carnotite 2 to 4 Autunite 2 to 2.5

By subjecting the ore to a scuing or `scr-ubbing type of grinding, the uranium values may be removed from the surface of the sand and silt particles. Desirably a grinding method is employed which selectively causes the softer interstitial material to be ground rather than the hard sand grains. Thus grinding methods which selectively crush or grind the larger grains regardless of hardness, for example, jaw Crushers, -ball mills, and cone grinders, are relatively ineffective for this purpose. Grinding techniques are preferred which cause the material undergoing treatment to grind itself. Autogenous grinding or autoattrition methods which cause the sand grains to act as grinding agents for the softer interstitial material include for example, impingemient, fluid energy grinding, jet grinding, tumbling and rolling. After grinding by an autoattrition method, the ore may be separated into coarse and fine fractions by conventional size separation techniques, the coarse fraction being of relatively lean uranium content and the fine fraction being of relatively rich uranium content.

Conventional methods of separating fine solid Vfractions from coarse fractions, for example, screening or centrifugal separation, may be used to concentrate the uranium yalues in the tine fraction. The line fraction is readily treated by hydrometallurgical techniques for further rening. In an example of crushing and screening a uranium ore containing 0.1 percent uranium, the following fractions are produced.

Screen size 1 Weight percent uranium 60 to 100 mesh .O2 to 200 mesh .02 200 to 325 mesh .l2 325 mesh and smaller .44

1Screen size here and throughout this specification and claims are Tyler Standard Screen Scale.

However, separation of uranium in scuing processes is not complete and some uranium values remain associated with the particles of sand and silt comprising the coarse fraction. Advantageously, the remaining uranium in the coarse sand fraction may be stripped therefrom by treating the coarse fraction 'with a substance reactive with the uranium constituents of the ore to form a sublimable cornpound at a temperature such that a sublimable compound is formed and condensing said sublimable compound by contact with the line fraction to further enrich the line fraction and recover substantially all of the uranium values of the ore. Substances reactive lwith the uranium constituents of ores to form sublimable compounds include halogens and halogen compounds for example, ammonium fluoride and ammonium biuoride.

The process of this invention may be applied to the separation of uranium values from natural ores as rwell as from mixtures of uranium with other materials which may be produced artificially.

FIGURE l is a diagrammatic representation of a method of separating uranium values from an ore fraction.

FIGURE 2 is a diagrammatic representation of a method of concentrating uranium values in an ore fraction.

Although the drawings illustrate arrangements of apparatus in lwhich the process of this invention may be practiced, it is not intended to limit the invention to the particular apparatus or materials described.

Referring to FIGURE l, a pulverulent uranium ore in hopper 1 and ammonium uoride from hopper 2 are passed through lines 3 and 4 respectively and combined in line 5. The ore and ammonium uoride in admixture are introduced through line 5 into kiln 8. Kiln 8 is heated by burning air and fuel from lines 9 and l0 in burner 1.1. The ore and ammonium uoride are introduced at the upper end of the kiln and are passed counter-current to the hot combustion gases from the gas burner at the lower end of the kiln. Hot ilue gases containing an excess of oxygen pass over the uranium ore oxidizing any tetrayalent uranium to the hexavalent or uranyl form. 'Ihe uranium present in the ore reacts with the ammonium -uoride to form volatile uranyl ammonium pentafluoride which is discharged from the lkiln with the gases in line 11. The hot kiln gases are passed into condenser 12 wherein the uranyl ammonium `pentafluoride is solidified. Solid uranyl ammonium pentafluoride is discharged through line 15 for use or further processing not shown. Flue gas is discharged through line 16 into water scrubber i7 'wherein the ue gases are contacted with water introduced through line 20 for the removal of traces of uranyl ammonium pentafluoride. Scrubbed flue gas is discharged through line 21. Water containing traces of uranyl ammonium pentauoride is discharged through line 22 to recovery facilitiesnot shown. Barren ore, substantially free of uranium values, is discharged from kiln 8 through line 25 `for disposal or recovery of other metal values not shown.

With reference to FIGURE 2, ore in hopper 50 is passed through line 5.1 to attrition grinder 52. In attrition grinder 52, the ore is pulverized by impingement grinding which effects more rapid grinding ofthe soft components of the ore than the hard components. The ore is 'ground to a particle size range such that about 50 percent passes a- 200 mesh sieve and 100 percent passes a 60 mesh sieve. Fine -ground ore is discharged through line 53 to sieve 55. In sieve 55, the ore is separated into two fractions, a coarse fraction retained on a 200 mesh screen which is discharged through line 56 and a tine fraction passed by a 200 mesh screen which is discharged through line 57.

The coarse ore from line 56 is discharged'into kiln 57 wherein it is contacted in counter-current ow with hot ue gases produced by 'burning fuel from line 60 and air from line 61 in burner 62. Ammonia gas from line 63 and iluorine gas from line 64 are introduced into the lower end of kiln 57 and react with the uranium values of the coarse ore to form uranyl ammonium pentafluoride. Hot ilue gases containing volatile uranyl ammonium fluoride are discharged through line 70.

The ine ore fraction from sieve 55 is discharged into cooler 71. The hot flue gases containing uranyl ammonium fluoride in line 70 from kiln 57 are introduced into cooler 71 and contacted with the cold line ore particles therein. The gas stream is cooled by contact with the fine ore and the uranyl ammonium pentafluoride condenses as a solid on the ore particles. -Flue gases freed of uranium ammonium pentafluoride are discharged through line 72. Ore, enriched in uranium values, is discharged through line 73 for further processing or use not shown.

Example 1 An ore containing 0.1 percent uranium is processed for the recovery of uranium values. The ore is crushed and ground to pass a 20 mesh screen in conventional crushing and grinding equipment. The 20 mesh ore fraction is then further ground in an air jet attrition grinder to pass a 60 mesh screen. The attrition mill products are then classifiedV to separate a coarse fraction having a particle size retained on a 325 mesh screen and a ne fraction passing a 325 mesh screen. The ne fraction comprises 7.5 percent of the uranium ore and contains 0.44 percent uranium. The coarse fraction comprises 92.5 percent of the total ore and contains 0.07 percent uranium. The coarse fraction is then admixed with ammonium fluoride at a rate of 0.11 pound of ammonium iluoride per pound of coarse ore and heated in a kiln in contact with hot combustion gases containing 7.9 percent oxygen. Barren ore containing 0.01 percent uranium is discharged from the kiln. Hot flue gases from the kiln containing uranyl ammonium pentailuoride are withdrawn and condensed in the presence of the line ore fraction to produce a iine ore concentrate having a uranium content of 1.3'weight percent.

Example 2 A Dakota lignite containing 0.1 percent uranium is processed for the generation carbon monoxide and hydrogen and for recovery of the uranium values. The lignite has a proximate analysis Vof about 30 percent moisture, 29 percent volatile matter, 29 percent fixed carbon and l2 percent ash. The lignite is reacted with steam and oxygen` a per square inch gage and at an autogenous temperature of 2050 F. Gas of the following composition is obtained:

Mol percent, dry fbasis Additionally, 106 pounds of slag comprising 0.72 weight percent uranium as UaOs and 14.3 weight percent carbon is withdrawn from the -gas generation zone as a slurry in fwater. Ammonium'fluoride is dissolved in the slag slurry and the slurry is then passed into a heating zone where the Water is vaporized and ammonium fluoride is decomposed to ammonia gas and hydrogen fluoride gas forming a dispersion of slag particles in vapor. The slag dispersion is then passed through an attrition grinding zone and into a kiln. Air is introduced with the slag dispersion to provide an oxidizing atmosphere and further heats the slag dispersion yby burning the carbon constituent of the slag. Under the high temperature oxidizing conditions of the kiln, the ammonia and hydrogen fluoride react with the uranium values of the slag forming volatile uranyl ammonium pentafluoride. The slag is separated from the vapors products 'which are separately cooled and solid uranyl ammonium pentaiiuoride is precipitated therefrom.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made Without departing from the spirit and scope thereof, and therefore only such limitations should lbe imposed as are indicated in the appended claims.

I claim:

l. In a process for concentrating uranium Ivalues of a uranium containing material the improvement which comprises contacting said material with a fluoride selected from the group consisting of ammonium fluoride and ammonium bifluoride in the presence of a free-oxygen containing gas at a temperature of at least 400 F., effecting formation of uranyl ammonium pentailuoride in vapor form, separating vapor comprising uranium ammonium pentafluoride and cooling said vapor etecting formation of solid uranium ammonium pentafluoride. Y

2. In a process for concentrating uranium values of av uranium containing material the improvement which comprises contacting said material with a fluoride selected from the group consisting of ammonium fluoride and ammonium bifluoride in the presence of a free-oxygen containing gas at a temperature of at least 400 F., effecting formation of uranyl ammonium pentauoride in vapor form, separating vapor comprising uranyl ammonium pentauoride and cooling said vapor in contact with a pulverulent solid effecting deposition of uranyl ammonium pentafluoride on said pulverulent solid.

3. In a process for concentrating uranium values of a uranium containing material the improvement which comprises contacting said material with a uoride selected from the group consisting of ammonium iluoride and ammoniumk bifluoride in the presence of a free-oxygen containing gas at a temperature of at least 400 F. eiecting formation of uranyl ammonium pentauoride in vapor form, and separating vapor comprising uranium ammonium pentauoride from a solid residue.

4. A methodof treating a uranium ore which comprises crushing said ore to pass a 60 mesh screen, classifying crushed uranium ore into a coarse fraction and a ne fraction, contacting said coarse ore fraction with a uoride selected from the group consisting of ammonium iluoride and ammonium biuoride in the presence of a free-oxygen containing gas at a temperature of at least 400 F. effecting formation of a sublimable uranium compound, separating said sublimable compound as a vapor from a solid ore residue, and condensing said sublimable uranium compound in Contact with said iine fraction.

(References on following page) References Cited in lche le of this patent UNITED STATES PATENTS Adams ..2 Aug. 12, 1913 McCoy Aug. 22, 1916 DAdrian Nov. 7, 1922 Gaither- May 15, 1945 Dunn et a1. July 24, 1951 McDuie et a1. Dec. 25, 1951 6 Seaborg May 19, 1959 Sellers July 18, 1961 OTHER REFERENCES Copenhofer: AEC Document NYC-5027, 7 pages, I anuary 30, 1943, declassied February 26, 1957.

Katz et al.: Chemistry of Uranium, pp. 111-122 and 365 (1951), McGraw-Hill Book Co., New York.

Van Impe: Chem. Eng. Prog., v01. 50, No. 5, May 1954,

Seaborg et al. May 6, 1958 10 pp. 230-234. 

1. IN A PROCESS FOR CONCENTRATING URANIUM VALUES OF A URANIUM CONTAINING MATERIAL THE IMPROVEMENT WHICH COMPRISES CONTACTING SAID MATERIAL WITH A FLUORIDE SELECTED FROM THE GROUP CONSISTING OF AMMONIUM FLUORIDE AND AMMONIUM BIFFURIDE IN THE PRESENCE OF A FREE-OXYGEN CONTAINING GAS AT A TEMPERATURE OF AT LEAST 400* F., EFFECTING FORMATION OF URANYL AMMONIUM PENTAFLUORIDE IN VAPOR FORM, SEPARATING VAPOR COMPRISING URANIUM AMMONIUM PENTAFLUORIDE AND COOLING SAID VAPOR EFFECTING FORMATION OF SOLID URANIUM AMMONIUM PENTAFLUORIDE. 